Method for making a balloon catheter stent deployment system

ABSTRACT

A balloon catheter and stent delivery system for medical treatment of a patient includes a balloon inflatable to an inflated shape having a cylindrical working portion, and a deflated shape that is temporarily reformed to enhance longitudinal retention of the stent while the catheter system is advanced or withdrawn. The balloon catheter provides for uniform expansion of the stent when the balloon is inflated. In addition, the balloon catheter system can be modified to initiate partial inflation of the proximal and distal ends of the stent, to further resist longitudinal motion of the stent during inflation, and to facilitate more effective tacking of the stent. One possible feature of the catheter system is that the balloon is pleated in a particular pattern when deflated, whereby the central balloon portion carrying the stent has a greater number of pleats than the shoulder portions proximal and distal of the stent. Another possible feature is the formation of small channels that facilitate fluid communication from the proximal end of the balloon to the distal end, even when the balloon is deflated. The balloon may be formed to protrude partially outward among the stent interstices while in its deflated state, further enhancing stent position retention. The present invention also protects the leading or distal end of the stent during advancement, and protects the proximal end of the stent during any withdrawal of the catheter system.

BACKGROUND AND SUMMARY OF THE INVENTION

1. Technical Background

The present invention relates generally to medical devices, and moreparticularly to a balloon catheter and stent delivery system.

2. Discussion

Balloon catheters are used in a variety of therapeutic applications,including intravascular catheters for procedures such as angioplasty.Nearly one million angioplasties were performed worldwide in 1997 totreat vascular disease, including coronary, neurological and peripheralblood vessels partially or totally blocked or narrowed by a stenosis. Byway of example, the present invention will be described in relation tocoronary and peripheral angioplasty treatments. However, it should beunderstood that the present invention relates to any balloon catheterand stent delivery system having enhanced stent retention, and is notlimited to angioplasty.

Most balloon catheters have a relatively long and flexible tubular shaftdefining one or more passages or lumens, and an inflatable balloonattached near one end of the shaft. This end of the catheter where theballoon is located is customarily referred to as the “distal” end, whilethe other end is called the “proximal” end. The balloon is connected toone of the lumens extending through the shaft for the purpose ofselectively inflating and deflating the balloon. The other end of thisinflation lumen leads to a hub coupling at the other end for connectingthe shaft lumens to various equipment. Examples of this type of ballooncatheter are shown in U.S. Pat. No. 5,304,197, entitled “Balloons ForMedical Devices And Fabrication Thereof,” issued to Pinchuk et al. onApr. 19, 1994, and also in U.S. Pat. No. 5,370,615, entitled “BalloonsCatheter For Angioplasty,” issued to Johnson on Dec. 6, 1994.

A common treatment method for using such a balloon catheter is toadvance the catheter into the body of a patient, by directing thecatheter distal end percutaneously through an incision and along a bodypassage until the balloon is located within the desired site. The term“desired site” refers to the location in the patient's body currentlyselected for treatment by a health care professional. After the balloonis disposed within the desired site, it can be selectively inflated topress outward on the body passage at relatively high pressure to arelatively constant diameter, in the case of an inelastic ornon-compliant balloon material.

This outward pressing of a constriction or narrowing at the desired sitein a body passage is intended to partially or completely re-open ordilate that body passageway or lumen, increasing its inner diameter orcross-sectional area. In the case of a blood vessel, this procedure isreferred to as angioplasty. The objective of this procedure is toincrease the inner diameter or cross-sectional area of the vesselpassage or lumen through which blood flows, to encourage greater bloodflow through the newly expanded vessel. The narrowing of the bodypassageway lumen is called a lesion or stenosis, and may be formed ofhard plaque or viscous thrombus.

Unfortunately, within approximately six months after angioplasty, thelumen at the angioplasty site may re-close or become narrow again. Thisphenomenon is called restenosis, and may occur in as many as 30-40% ofpercutaneous transluminal angioplasty patients. Restenosis may requirean additional procedure, such as another angioplasty, drug therapytreatment, or even surgery including bypass graft. It is of coursedesirable to prevent or limit the occurrence of restenosis, especiallysince some patients may not be preferred candidates for anotherinterventional treatment.

In an effort to prevent restenosis, short flexible cylinders orscaffolds made of metal or polymers, referred to as a stent, may bepermanently implanted into the vessel to hold the lumen open, toreinforce the vessel wall and improve blood flow. The presence of astent tends to keep the blood vessel open longer, but their use may belimited by various factors, including size and location of the bloodvessel, a complicated or tortuous vessel pathway, etc. Also, even avessel with a stent may eventually develop restenosis.

Some stents are expanded to the proper size by inflating a ballooncatheter, referred to as “balloon-expandable” stents, while others aredesigned to elastically resist compression in a “self-expanding” manner.Both balloon-expandable stents and self-expanding stents are generallycrimped or compressed to a diameter during delivery that is smaller thanthe eventual deployed diameter at the desired site. When positioned atthe desired site within the lesion, they are deployed by inflating aballoon or being allowed to self-expand into the desired diameter.

Friction forces may tend to cause a crimped stent to slip in a proximaldirection while the catheter system is advanced, or to slip in a distaldirection if the physician decides to withdraw the stent withoutdeploying it. It is of course desirable to retain the stent in theproper position, during advancement along a vascular path to the desiredsite.

Accordingly, it is an object of the present invention to provide ballooncatheter systems for enhanced stent position retention duringlongitudinal movement of the catheter.

It is a further object of the present invention to provide methods formaking balloon catheter systems having enhanced stent positionretention.

These and various other objects, advantages and features of theinvention will become apparent from the following description andclaims, when considered in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a balloon catheter having astent mounted around the balloon, arranged according to the principlesof the present invention;

FIG. 2 is a longitudinal cross-section view of the balloon catheter andstent of FIG. 1;

FIG. 3 is a transverse cross-section view of the balloon catheter andstent of FIG. 2, taken along line 3—3;

FIG. 4 is a longitudinal cross-section view of a balloon catheter andstent, according to the prior art;

FIG. 5 is a partial longitudinal cross-section view of a deflatedballoon catheter and stent, arranged according to the principles of thepresent invention;

FIG. 6 is a partial longitudinal cross-section view of a partiallyinflated balloon catheter and stent;

FIG. 7 is a partial longitudinal cross-section view of a fully inflatedballoon catheter and stent; and

FIGS. 8-12 illustrate a method for making the balloon catheter stentdelivery system of the present invention.

FIGS. 13-15 are longitudinal cross-section views of a catheter systemshowing stages in assembly;

FIG. 16 is a perspective view of a balloon catheter; and

FIG. 17 is a tranverse cross-sectional view of a pleated ballooncatheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiments of the presentinvention is merely illustrative in nature, and as such it does notlimit in any way the present invention, its application, or uses.Numerous modifications may be made by those skilled in the art withoutdeparting from the true spirit and scope of the invention.

Referring to the drawings, a balloon catheter system is depicted, withone of the preferred embodiments of the present invention being showngenerally at 10. The balloon catheter of FIG. 1 has an inflatableballoon 12, a relatively long and flexible tubular shaft 14, and a hub16. The balloon is affixed to the shaft near a distal end of the shaft,and the hub is affixed to the proximal end of the shaft.

The shaft defines one or more passages or lumens extending through theshaft, at least one of which is an inflation lumen connected to theballoon for the purpose of selectively inflating and deflating theballoon. The inflation lumen thus provides fluid communication betweenthe interior of the balloon at the distal end of the inflation lumen,and a hub inflation port having a coupling or luer-lock fitting at theproximal end for connecting the inflation lumen to a source ofpressurized inflation fluid (not shown) in the conventional manner.

In the illustrated embodiment, the shaft is constructed of an inner andouter tubular body 18 and 20. The inner body defines a guidewire lumen,while the inflation lumen is defined by the annular space between theinner and outer tubular bodies. The guidewire lumen is adapted toreceive an elongated flexible guidewire in a sliding fashion, such thatthe guidewire and catheter may be advanced or withdrawn independently,or the catheter may be guided along a path selected with the guidewire.The shaft may of course have various configurations instead of thiscoaxial design, including a single extruded tube defining any suitablenumber of parallel side-by-side lumens, a proximal shaft portion formedof a metal hypotube, and others.

The proximal hub is affixed to the proximal end of the shaft, andprovides an inflation port and a guidewire port, again with a luer-lockfitting or hemostatic valve. Such a valve allows the guidewire totraverse and slide within the guidewire lumen, yet while resisting theloss of blood or other fluids through the guidewire lumen and guidewireport. As shown in the drawings, the inner and outer tubular bodies aresecurely received within the hub, and surrounded by a tubular strainrelief. The hub provides fluid communication between the guidewire lumenand a guidewire coupling, as well as between the annular inflation lumenand the inflation coupling.

A stent 22 of any suitable type or configuration may be provided withthe catheter of the present invention, such as the well-knownPalmaz-Schatz balloon expandable stent. Various kinds and types ofstents are available in the market, and many different currentlyavailable stents are acceptable for use in the present invention, aswell as new stents which may be developed in the future. The stentdepicted in the drawings is a cylindrical metal mesh stent having aninitial crimped outer diameter, which may be forcibly expanded by theballoon to a deployed diameter. When deployed in a body passageway of apatient, the stent may be designed to preferably press radially outwardto hold the passageway open.

As shown in the drawings, the balloon in its fully inflated profileshape has a cylindrical working portion with an inflated diameterlocated between a pair of conical end portions, and a pair of proximaland distal legs affixed to the shaft. The balloon in its deflatedprofile shape preferably has several pleats that are wrapped around theshaft. The balloon material is preferably substantially inelastic, andstretches a relatively small amount under pressures of 15 atmospheres ormore. Various different materials may be used, including Nylon, PEEK,PEBAX material, or a block copolymer thereof.

The novel method of making the balloon catheter system of the presentinvention provides several advantages. Among these advantages is thatthe balloon has a composite profile shape which varies at differentpressures. The balloon initially is in a deflated state and has adeflated profile shape, as specifically illustrated in FIG. 5, having acentral bed portion with a deflated bed diameter being flanked by a pairof proximal and distal shoulders or puffs 26 and 28 defining deflatedshoulder diameters that are larger than the deflated bed diameter.

The balloon shoulders or puffs 26 or 28 smoothly taper in proximal anddistal directions respectively to proximal and distal legs that areaffixed to the shaft. This deflated balloon profile shape thus providesa bed or nest portion for receiving the stent and tending to hold thestent in place, while minimizing friction or adverse contact between theends of the stent and the blood vessel wall. The present invention thustends to protect the leading or distal ends of the stent duringadvancement into the patient's body, and the proximal end of the stentduring any withdrawal of the catheter system.

As specifically shown in FIG. 6, while the balloon is inflated atintermediate pressures, it will tend to exhibit nested profile shapessimilar to the original deflated and nested profile shape of FIG. 5. Onepossible feature of the present invention is the formation of smallchannels that facilitate fluid communication from the proximal end ofthe balloon to the distal end, even when the balloon is deflated. Theballoon thus tends to inflate more uniformly along its length, such thatboth proximal and distal balloon shoulders inflate at substantially thesame times and pressures.

In addition, the present balloon catheter system can be modified toinitiate partial inflation of the proximal and distal ends of the stent,to further resist longitudinal motion of the stent during inflation, andto facilitate more effectively fixing the stent in place within theblood vessel, called “tacking” the stent.

FIG. 7 depicts the balloon in its fully inflated profile shape. Thestent bed shape disappears, and the balloon profile shape changes ormorphs into a different profile shape when inflated at full inflationpressure. This fully inflated shape provides the preferable cylindricalworking portion, wherein the portion of the balloon supporting andexpanding the stent has an inflated diameter larger than any otherportion of the balloon. This feature tends to prevent any part of theballoon from expanding excessively, which might cause local trauma tothe blood vessel wall.

Accordingly, the portions of the present balloon reverse positions. Thecentral bed portion initially has a smaller deflated diameter than theproximal and distal shoulders 26 and 28, which provides a desirablysmall outer maximum diameter for ease of insertion. The initial outermaximum diameter is referred to as the “primary profile.” In contrast,the central balloon portion expands on full inflation to the largestdiameter of the balloon, while the portions that previously formed theballoon shoulders 26 and 28 expand comparably less. Indeed, the formershoulders 26 and 28 define the proximal and distal end conical portionsof the fully inflated profile shape.

In the deflated shape, the balloon is therefore temporarily reformedinto a different shape than what might conventionally result from simplydeflating and pleating a previously known balloon. This temporarilyreformed shape enhances stent position retention, and yet exhibits thepreferable fully inflated shape. The balloon of the present inventionalso tends to reduce the maximum profile diameter after the balloon isdeflated, referred to as the “secondary profile.”

The balloon catheter system of the present invention may be made usingany of the following methods, as well as various modifications that willbe apparent to those skilled in the art. The balloon is folded into anysuitable or preferable number of longitudinal pleats which are wrappedaround a portion of the catheter shaft, either manually or by using apleating machine.

The balloon is then temporarily held in its pleated condition byslipping a forming tube in the proximal direction onto the pleatedballoon, while the assembly is transported to the next processingstation. The pleated balloon may be allowed to sit overnight, which mayimprove its tendency to hold its pleated shape. After the forming tubeis removed, a stent is slipped onto the pleated balloon. The stent isthen gently crimped or compressed around the balloon, with the pleatsintact, to a crimped condition in which the stent has a crimped outerdiameter.

The resulting balloon catheter and stent assembly is then placed in atubular mold 32, having an internal diameter slightly greater than thecrimped outer diameter of the stent. The tubular mold should have aconstant inner diameter, to cause the balloon shoulders 26 and 28 tohave the preferred shape and diameter.

The balloon is then pressurized by applying a pressurized gas or fluidto the inflation port and through the inflation lumen. The preferredpressure of the inflation within the tubular mold may slightly exceedthe rated burst pressure of the balloon, and the mold will preventexpansion of the stent while allowing the proximal and distal balloonshoulders 26 and 28 to form. The pressurized fluid may preferably be drynitrogen, and the pressure may preferably be maintained for apreselected period of time, such as several minutes.

While mold with the accompanying balloon catheter and stent assembly isheld under pressure, they are then held in a hot liquid bath, forseveral purposes. First, the heat tends to set the stent in place, thusforming the desired proximal and distal shoulders. Second, if theballoon is made of Nylon according to one of the preferred embodiments,then the water of the heating bath tends to hydrate the Nylonplasticizer of the balloon material. Of course, a hot air system mayalso be used. The preferred temperature of the heated water bath ispreferably below the permanent deformation temperature of the balloonmaterial, and the time and pressure of this process may be extended toensure that such a temperature will result in the desired compositeshape and temporary reformation of the balloon.

The balloon, stent and mold assembly is then removed from the heatedliquid bath, while the pressure is maintained for a period of time.After the pressure is relieved, the mold is then removed, and theballoon and stent assembly may be dried and again heated by applying ahot air gun for a period of time.

Several features of this preferred method of making the balloon catheterstent delivery system of the present invention have some importance tothe performance of the resulting product, including the temperatures,pressures, time periods, crimped outer diameter of the stent, theinternal diameter of the mold, as well as the thermal characteristics ofthe balloon, stent and mold.

The particular preferred method described above for making a ballooncatheter stent delivery system obviously produces a balloon catheterhaving an already mounted stent. However, the methods of the presentinvention may also be used to produce a balloon catheter having thedesired enhanced stent retention capability, without incorporating anincluded stent. Accordingly, the physician may then install and manuallycrimp any selected stent having the proper dimensions, while yet takingadvantage of the enhanced stent position retention of the presentinvention. Also, this modified method of making the balloon of thepresent invention may be modified to produce balloon shoulders that havea greater initial outer diameter than that of the stent.

Accordingly, a balloon catheter having enhanced stent position retentionmay be made, without requiring a stent during the process, by a methodsimilar to that described above. During this modified method, thepresence of a stent is obviated by replacing it with a ‘phantom stent.’One advantage of using a phantom stent is that it costs much less thanan actual metal stent. Such a phantom stent 30 may be formed of anysuitable plastic material capable of withstanding the temperatures andpressures of the manufacturing method without melting or deforming.Suitable plastic materials for the phantom stent may thus include forexample, PTFE or polyethylene.

Since the plastic phantom stent will not crimp in the same way that anactual metal stent does, it must be provided with a longitudinal slit orpreferably a spiral cut. The phantom stent may thus be installed ontothe pleated balloon, and removed after forming the stent nest with theaccompanying shoulders, by way of the cut in the plastic material.

When a balloon catheter is made and processed according to the methodsof the present invention, and then the phantom stent is removed, theresulting balloon catheter has a stent nest or bed portion which willprovide enhanced stent position retention for any stent of suitabledimensions.

Indeed, the size of the resulting balloon shoulders 26 and 28 may betailored by carefully selecting the tubular wall thickness of theplastic phantom stent to be greater than the wall thickness of thestent.

It should be understood that an unlimited number of configurations forthe present invention could be realized. The foregoing discussiondescribes merely exemplary embodiments illustrating the principles ofthe present invention, the scope of which is recited in the followingclaims. Those skilled in the art will readily recognize from thedescription, claims, and drawings that numerous changes andmodifications can be made without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A method for making a balloon catheter stentdeployment system, comprising the steps of: providing a balloon catheterwith an elongated flexible shaft having proximal and distal ends, a hubaffixed to the shaft proximal end and having an inflation port, and aninflatable balloon affixed to the shaft near the shaft distal end; theshaft defining an inflation lumen providing fluid communication of aninflation fluid between the hub inflation port and the balloon, suchthat the balloon is adapted for selective inflation from a deflatedstate to an inflated state, as well as later deflation; the balloonbeing formed of a substantially inelastic material; the balloon having acylindrical working portion with an inflated cross-sectional arealocated between a pair of conical portions and a pair of leg portionswhen the balloon is in the inflated state; pleating the balloon in adeflated state into multiple longitudinal pleats and wrapping the pleatsaround a portion of the shaft; providing a cylindrical phantom stentdefining a tubular wall thickness; mounting the phantom stent around theballoon; inserting the balloon and phantom stent into a tubular molddefining a single inner diameter throughout its working length;pressurizing the balloon with a pressurized fluid to a first pressure,and simultaneously heating the balloon, phantom stent and mold; therebycausing the balloon to form a first and second shoulder locatedimmediately proximal and distal of the phantom stent; each balloonshoulder having an initial outer diameter equal to the initial outerdiameter of the phantom stent; such that the balloon defines an indentednest shape for the stent in the deflated state; removing the balloon andphantom stent from the mold; removing the phantom stent from the ballooncatheter; and providing a cylindrical medical stent having a wallthickness less than the phantom stent wall thickness; sliding themedical stent over the balloon and crimping the medical stent around theballoon; such that the balloon shoulders have an outer diameter greaterthan an outer diameter of the crimped medical stent; wherein the balloonis temporarily reformed into a modified shape, and is adapted to inflateand expand the stent to a deployed larger diameter, whereby the balloonforms said cylindrical working portion at above a preselected transitionpressure, such that the cylindrical working portion and the portionsdefining the balloon shoulders in the deflated state have substantiallythe same diameter in the inflated state; thereby causing said indentednest shape to substantially disappear.
 2. The method of claim 1, whereinthe phantom stent is made of a polymer material, and the medical stentis metal.
 3. The method of claim 1, wherein the phantom stent has a cutextending from a proximal end to a distal end of the phantom stent, forfacilitating removal of the phantom stent from the balloon.
 4. Themethod of claim 1, wherein the phantom stent and the medical stent haveequal lengths, such that after the step of crimping, the balloonshoulders are located immediately proximal and distal of the medicalstent.